Hideaki Nakashima

The Effects of Temperature and Dinitrophenol on the Change of the Proportion of Pfr Controlling RNA Synthesis in Lemna gibba G3 in a Prolonged Dark Period

Summary Pfr level regulating RNA synthesis in dark period was estimated by the null response method in a long-day duckweed, Lemna gibba G3. In spite of culture at different temperatures (20 to 33 °C) and of the presence of DNP, this level began to decrease at the same time (about 22nd hr after beginning of the dark period) and the lowering rate was constant. In the culture at 16 OC, however, Pfr level was high even at the 37 th or 61st hr of the dark period. The characteristics of the system holding high Pfr level, at usual temperatures, were similar to those of the physiological clock.

The Effects on RNA Synthesis in a Long-Day Duckweed, Lemna gibba C 3, of Irradiation with Different Ratios of Red and Far Red Light During the Prolonged Dark Period

Summary Changes in the proportion of Pfr in the long-day duckweed Lemna gibba G3 during the dark period were examined using the null response method. The dark period was interrupted for 5 minute periods at various times by lights containing different ratios of both red and far red light at an intensity of 120 µW/cm 2 . RNA synthesis was then determined at selected times following irradiation. The dark period can be divided into 3 different periods each of which has a different sensitivity to the mixed lights. The duckweed irradiated with 100 % red light showed the same or slightly stimulated RNA synthetic activity as the dark control up to the 22nd hour from the beginning of the dark period: the value of null % red was 100 % or near. The value of null % red then decreased rapidly during next 12 h period to a constant level of 40 % red and finally remained at this level until the 37th hour. We concluded that phytochrome can modulate the amplitude of RNA synthesis rhythm, but that since the Pfr level remained high until the 22nd hour from the beginning of the dark period, the diurnal change of RNA synthetic activity during the dark period is not a direct result of fluctuations in the Pfr level.

The Effects of Calcium Withdrawal on the Uridine Uptake Process in a Long-day Duckweed, Lemna gibba G3

Summary The effects of calcium withdrawal on the process of uridine uptake was examined in a long-day duckweed, Lemna gibba G3. A short term treatment in sodium citrate reduced the rate of uridine uptake. It changed the value of Vmax for uridine uptake more than that of Km. CaCl2 was the most efficient compound in offsetting the citrate reduction. Sodium citrate did not, however, change the pattern of intracellular conversion of uridine absorbed into the duckweed cells. The lowered uptake rate recovered completely after 12 h when the duckweeds were cultured in the normal culture medium. The recovery process was inhibited by compounds which normally inhibit protein synthesis, although they did not change the rate of leucine transport into the duckweed or the activity of uridine phosphorylation. We concluded from these experiments that the protein(s) necessary for the uridine transporting system were released from the duckweed by treatment with sodium citrate and that calcium may be necessary for the molecular connection of the uridine transporting protein(s) to the cell membrane.